A latent fingerprint is one in which the shape of raised portions of skin (fingerprint ridges) with secretion attached thereto at a fingertip or the like are transferred to a specimen, such as a piece of evidence. The latent fingerprint contains, besides moisture that is the main ingredient, salt such as sodium chloride, lactic acid, amino acids, uric acid, protein, and vitamins. A latent fingerprint detection becomes an evidential matter necessary for determining, arresting, and prosecuting a criminal, thus being an important means for criminal investigation.
Conventional methods for detecting a latent fingerprint employ chemical reaction and physical adsorption reaction with fingerprint ingredients. Specifically, there are a powder method in which fine powder of aluminum, lycopodium, or the like is attached to moisture or fat in the fingerprint ingredients so as to use a color tone difference between the specimen and the powder, and a liquid method in which amino acid and salt contained in the fingerprint ingredients are reacted with chemicals so as to cause coloration.
With the powder method, the surface of the specimen to which a fingerprint is attached or the fingerprint seems to be attached is lightly brushed with a brush dusted with aluminum powder so that the aluminum powder is attached to the fingerprint, and the fingerprint is transferred to a gelatin sheet. However, in the process of applying the fine powder of aluminum or the like to the entirety of a region including the latent fingerprint, other fingerprint or the like may be mixed and contaminated, thus being obstructive to the case of conducting a DNA test after detecting the fingerprint. In the criminal investigation, if the specimen is a specific material, for example, a metal murder weapon such as pistol and knife, a synthetic leather, and an adhesive surface of a tape, it may be difficult to transfer a clear fingerprint.
With the liquid method, a specimen with a latent fingerprint needs to be immersed in a chemical solution, and hence it is unsuitable for detecting a fingerprint at a location that cannot be moved, such as walls. There are also the problems that the latent fingerprint may be washed away with the chemical solution, and that the specimen including the latent fingerprint may also be stained. It is therefore desired to achieve a technology of surely detecting the fingerprint without directly contacting the specimen.
As a detection method in place of the powder method or the liquid method, there is, for example, a fingerprint detection method (cyanoacrylate method) using 2-cyanoacrylic acid ester (monomer), which is one of gas methods suitable for a weak latent fingerprint and a specimen that is apt to change with a solvent or the like. The cyanoacrylate method has already been put to practical use in Japan and overseas. The cyanoacrylate method is intended for actualizing the latent fingerprint by polymerizing the 2-cyanoacrylic acid ester on the latent fingerprint region so as to form white solidification. The cyanoacrylate method is capable of restoring a clearer fingerprint trace, however, it may be difficult to ensure detection on a whitish specimen, such as a shopping bag and aluminum foil, because 2-cyanoacrylic acid ester polymerized on the latent fingerprint is transparent or white.
Hence, in order to improve the disadvantage of the cyanoacrylate method, a method has been proposed which includes bringing a fluorescent aye into contact during or after the 2-cyanoacrylic acid ester processing.
For example, with the fingerprint detection method disclosed in Patent Document 1, after the evaporated 2-cyanoacrylic acid ester is brought into contact with the surface of a test object so as to be gradually deposited thereon, a solution in which a fluorescent dye is dissolved in an organic solvent is brought into contact with the specimen, and the solution on the surface of the test object is dried, thereby detecting a fingerprint as a fluorescent fingerprint.
With the fingerprint detection method disclosed in Patent Document 2, a specimen having a fingerprint detected thereon is exposed to vaporization atmosphere of 2-cyanoacrylic acid ester and a sublimation dye, thereby detecting a colored fingerprint image.
With the polymer for detecting a fingerprint, the method for producing the same, the composition for detecting a fingerprint, and the fingerprint detection method using them, which are disclosed in Patent Document 3, 2-cyanoacrylic acid ester is polymerized using a specific fluorescent dye as a polymerization initiator, thus allowing the 2-cyanoacrylic acid ester and the fluorescent dye to be attached to a latent fingerprint at a low depolymerization temperature in a single step. This ensures a clear fluorescence detection even on the whitish specimen, such as the shopping bag and aluminum foil, which have been difficult to detect so far.